Echinocandins and echinocandin-like cyclohexapeptide compounds are described in the literature as highly effective antifungal agents, particularly against yeasts causing mycotic infections such as Candida albicans, Candida parapsilosis and the like. Some of these compounds are natural products produced by cultivation of microorganisms such as Aspergillus rugulosus, Aspergillus nidulans or Acrophialophoria lemonispora described in U.S. Pat. Nos. 4,024,245, 4,024,246 and 4,173,629, respectively. Some of these compounds are semi-synthetic obtained by modifying the natural products such as described in U.S. Pat. Nos. 4,287,120, 4,293,487, 4,293,489, 4,320,053, 4,370,054 and 4,322,338. The latter semi-synthetic compounds were generally prepared by deacylating the lipophilic side chain attached to an amino substituent on the cyclohexapeptide nucleus and thereafter reacylating to obtain modified cyclopeptides in which the lipophilic side chain was different but in which the cyclohexapeptide nucleus stayed basically the same.
The echinocandin type cyclohexapeptide compounds are generally unstable in aqeuous medium. During a search for echinocandin type cyclohexapeptide compounds, it was found that modifying the formula by reducing certain hydroxyl groups would produce a more stable compound. In Helvetica Chimica Acta 62, 1252, 1267 (1979), there is described reduction of certain hydroxyl groups in tetrahydroechinocandin B and tetrahydroechinocandin C. It is, however, a multistep procedure and, a selective reduction has not been demonstrated. Thus, when tetrahydroechinocandin B is the starting material, a bis-reduced product is obtained by a two step procedure in which the thioether intermediate must be isolated and thereafter reduced: ##STR3##